Re: [PATCH 01/12] mm/huge_memory: zap deposited page tables after an RCU grace period

On Tue, Sep 01, 2026 at 06:11:57PM +0100, Kiryl Shutsemau wrote:
> On Tue, Sep 01, 2026 at 04:45:14PM +0100, Lorenzo Stoakes (ARM) wrote:
> > > munmap() of 64G worth of THP should be enough to demonstrate the
> > > problem.
> >
> > I mean you're going to hit that from RCU freeing page tables already, which
> > most architectures already do right?
>
> Not at the same rate -- tlb_remove_table() batches into struct
> mmu_table_batch. One call_rcu() per MAX_TABLE_BATCH.
>
> > So if RCU saturation is a problem, that problem already exists, but I've
> > not heard of that being a problem at all?
>
> I did quick test and I don't see a measurable difference in munmap()
> wall time of 40G of THPs. I see ~17x more softirqs, but this is
> expected.
>
> The objection is retracted.
>
> We can return to this later if it is going to be visible anywhere.

Great thanks! :)

>
> --
>   Kiryl Shutsemau / Kirill A. Shutemov

--
Cheers, Lorenzo